Conventional hydride-based batteries provide a low-cost energy storage system. For example, conventional nickel-metal hydride (MH) batteries include a positive electrode containing nickel hydroxide, a negative electrode containing metal hydride, a separator between the positive and negative electrodes and an alkaline electrolyte. The electrolyte commonly includes an aqueous solution of potassium hydroxide. Charge and discharge reactions for nickel metal hydride batteries may be written as:
Positive electrode:Ni(OH)2+OH−→NiOOH+H2O+e− (charge)  (1)NiOOH+H2O+e−→Ni(OH)2+OH (discharge)  (2)
Negative electrode:M+H2O+e−→MHab+OH− (charge)  (3)MHab+OH−→M+H2O+e− (discharge)  (4)where M is a hydrogen storage alloy and Hab is absorbed hydrogen.
However, the energy density of these batteries can be relatively low. For example, state-of-the-art metal hydride batteries can provide an energy density of approximately of 60˜100 Whr/kg.
Accordingly, there exists a continued need for higher capacity hydrogen storage alloys, which can lead to improved energy density of metal hydride/nickel batteries, and even more significantly, metal hydride-air batteries.